The present invention relates to a control system and method for controlling a turbo-charged throttled engine which consumes fuels such as gasoline, natural gas, LPG, hydrogen.
Heavy duty throttled engines, such as natural gas engines, are turbo-charged in order achieve diesel-like performance and power density. Such engines use fuel and air regulating devices which are controlled by the engine control unit (ECU). If the load on such an engine is rapidly reduced while the engine is operating in a highly boosted condition, this can dramatically reduce the flow rate through the turbocharger compressor over a short period of time. This results in a compressor surge condition, which can reduce turbocharger lifetime and produce objectionable noise.
Accordingly, an object of this invention is to provide a system for reducing turbocharger surge in an engine.
This and other objects are achieved by the control system of the present invention. The control system functions with a turbo-charged throttled engine having intake air compressor and an exhaust turbine which receives engine exhaust. The control system includes an air throttle between the compressor and the engine and a wastegate communicated with engine exhaust upstream and downstream from the turbine. The control system generates a desired air mass value per engine stroke value as a function of a desired fuel flow amount and a stored a compressor surge characteristic. The control system generates a desired manifold air pressure value as a function of the desired air mass value and sensed engine parameters. The control system controls the air throttle and the wastegate so that the actual manifold air pressure matches the desired manifold air pressure. This system eliminates turbocharger surge and its effect on turbocharger durability. By eliminating turbocharger surge, the objectionable noise noticed by the operator during load reduction transients is also eliminated or greatly reduced. A further advantage is elimination of turbocharger overspeed conditions which can be experienced during operation at high altitudes which also affects turbocharger durability. This strategy differs from the prior art in that it modulates the air controls to prevent transient surge and actively identifies and prevents turbocharger overspeed conditions.